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A polynuclear aromatic hydrocarbon is a compound of hydrogen and carbon that has two or more benzene rings. Some of the most common polynuclear aromatic hydrocarbons are naphthalene, pyrene, anthracene, and chrysene, among others.
What are hydrocarbons
Hydrocarbons are organic compounds that are formed only by carbon (C) and hydrogen (H) atoms. Hydrocarbons are divided into aromatics, also called arenes, and aliphatics, which in turn are classified into alkanes, alkenes, and alkynes.
Hydrocarbons are one of the main sources of energy for life today and most of them are found in crude oil.
aromatic hydrocarbons
Definition and characteristics
Aromatic hydrocarbons are a group of more than one hundred organic compounds that are formed by a six-carbon benzene ring joined by alternating double bonds. This allows them to have great stability. Also, it gives them a strong smell, and that is why they are called aromatic.
Depending on the number of benzene rings they have, aromatic hydrocarbons can be:
- Mononuclear: are those that have a single benzene ring.
- Polynuclear: are those that are formed by more than one benzene ring.
Rings are also called “cycles.” For this reason, aromatic hydrocarbons are also called monocyclic or polycyclic.
Likewise, according to the substituents that the benzene rings have, aromatic hydrocarbons can also be subdivided into monosubstituted or polysubstituted, if they have one or more substituents, respectively.
What are polynuclear or polycyclic aromatic hydrocarbons?
Polynuclear aromatic hydrocarbons, whose acronym is PAH, are compounds made up of carbon (C) and hydrogen (H) molecules that contain two or more benzene nuclei in their molecular structure. A very common example of this type of hydrocarbon is naphthalene, which is commonly known as naphthalene. It is used to combat moths and also in the manufacture of paints and varnishes.
Properties
Polynuclear aromatic hydrocarbons are characterized by having the following properties:
- In the solid state they can be white, yellow or pale green or colourless.
- They are nonpolar, that is, they do not have an unequal electrical charge.
- They do not dissolve easily in water.
- They are lipophilic, that is, they tend to bind to fats.
- They are toxic to living beings.
Examples of polynuclear aromatic hydrocarbons
There are numerous examples of polynuclear aromatic hydrocarbons. Some of the most common are:
- acenaphthene
- acenaphthylene
- ananthrene
- Anthracene
- Benzo[a]anthracene
- Benzo[a]pyrene
- Benzo[e]pyrene
- Benzo[b]fluoranthene
- Benzo[g,h,i]perylene
- Benzo[j]fluoranthene
- Benzo[k]fluoranthene
- Cyclopenta[c,d]pyrene
- chrysene
- dibenzo
- fluoranthene
- fluorene
- phenanthrene
- indene
- naphthalene
- pyrene
How Polynuclear Aromatic Hydrocarbons Are Formed
PAHs are formed when incomplete combustion of organic matter occurs, such as the incomplete burning of coal, oil, gas, waste, and other organic substances such as tobacco or meat cooked on coals. They are also formed from volcanic eruptions and forest fires.
In everyday life, the most common source of exposure to polynuclear aromatic hydrocarbons is tobacco smoke.
In the combustion process, organic matter, which is made up of carbon and hydrogen, reacts with oxygen, producing carbon dioxide and water. But if there is not enough oxygen, the combustion is incomplete, that is, part of the
fuel does not completely react with oxygen and other by-products such as carbon monoxide and polynuclear aromatic hydrocarbons are obtained as a result, which can be harmful to health. and even cause death.
health consequences
Polynuclear aromatic hydrocarbons are notorious for the damage they cause to health and the environment. Exposure to these chemicals is associated with genetic damage and cancer. In children it can cause asthma and a decrease in IQ.
The most common forms of exposure to PAHs occur through breathing contaminated air, eating foods that contain these compounds, and through direct skin contact.
In addition, there are some aromatic hydrocarbons that are considered carcinogenic. These include: benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, dibenzo[a,h]anthracene, and indene[1, 2,3-cd]pyrene.
Uses and applications of polynuclear aromatic hydrocarbons
Aromatic hydrocarbons have been used since the early 19th century. Currently, its application is common in industry, especially in the manufacture of plastics, paints, synthetic rubber, pesticides, explosives, detergents, pharmaceuticals and perfumes. They are also used as components of gasoline and some solvents.
In addition, benzene is used to make phenols, styrene, detergents, pharmaceuticals, fuel, and dyes.
Naphthalene is used to carry out the organic synthesis of various chemical substances such as moth repellent products and wood preservatives.
Chrysene is used as a component of asphalt to pave roads. Anthracene is included in the manufacture of insecticides and preservatives and to make anthraquinone, a dye substance. Pyrene is also used to make dyes and dyes.
Other Common Uses of Aromatic Hydrocarbons
- Cumene is used in jet fuels and as a solvent for cellulose paints and lacquers. p-Cymene is the component of various essential oils and is also used as a solvent.
- Coumarin is used in the production of deodorants and as an aroma enhancer in soaps, tobacco, rubber derivatives, and perfumes.
- Pseudocumene is used in the manufacture of perfumes.
- Toluene is one of the components of solvents for oils, resins, rubber and acetylcellulose, as well as detergents and dyes.
- Styrene is used to make various polymers, such as polystyrene.
- Xylene is used as a thinner for paints and varnishes, and in the production of pharmaceuticals.
- Terphenyls are used as coolants for nuclear reactors.
- Diphenylmethane is used as a soap flavoring and as a solvent for cellulose lacquers.
Bibliography
- Sharp, A. (2009). Polycyclic aromatic hydrocarbons (PAHs) . General Union of Workers. Ministry of Occupational Health and Environment. Spain. Available at: https://www.ugt-fica.org/images/proyectosl/sl/directa/2010/metal/Los%20Hidrocarburos%20Arom%C3%A1ticos%20Polic%C3%ADclicos%20HAP.pdf
- Olaya Querevalu, MT Aromatic hydrocarbons. (2019). Peru. QF Mario Teodoro Olaya Querevalu.
- Ramírez Gómez, LE Chemistry of carbon. (2020). Mexico. Leopoldo Eugenio Ramirez Gomez.
